1. Field of the Invention
This invention pertains to microelectromechanical systems (MEMS) actuators.
2. Description of the Related Art
Electrically controlled actuators receive an electrical signal input and provide a mechanical output. The mechanical output provides power (force times displacement, per unit time) that can be used to move objects. Large, electrically controlled actuators are common in mechanical systems to control valves, pumps, switches and otherwise move objects.
Recent innovations require control of very small components that are formed on semiconductor substrates by conventional semiconductor fabrication processes. Groups of such components are known as microelectromechanical systems (MEMS). MEMS borrow design elements from their larger, conventional-size, functional equivalents, but must be adapted to semiconductor fabrication techniques and the dynamics of miniature size. An often essential part of MEMS are actuators that provide physical movement or force to other MEMS components in order to operate, or initiate, the MEMS device.
In U.S. Pat. No. 5,808,384 a photolithographic process is used to fabricate a MEMS having an actuator that controls switches, relays, and valves. This actuator consists of a coil and magnetic core to move a member. However, this actuator is capable of only a very small range of motion and is thus limited to particular applications in which a relatively small range of motion is required.
Certain MEMS devices include relatively large planar objects that require a means to position the planar object for operation. In so-called xe2x80x9cbillboardxe2x80x9d applications, a planar object is formed flat against a supporting substrate and must be moved upright for use (i.e., oblique, or orthogonal, to the substrate)xe2x80x94similar to how a roadside advertising billboard is arranged relative to its supporting ground surface.
U.S. Pat. No. 5,867,297 discloses such a billboard application in relation to a prior art MEMS optical scanner in which a mirror is fabricated in the horizontal plane (i.e., parallel to the substrate upon which the mirror is formed) and then lifted into a substantially vertical arrangement. The U.S. Pat. No. 5,867,297 states that a comb drive may be used to facilitate the process of raising the billboard.
A known electrical device is a conductive coil. When current passes through the coil, a magnetic flux is generated in the coil. Further, when the magnetic flux is changing, an electromotive force (emf) may be induced in a conductive object located in the path of the coil""s magnetic flux. The induced emf further creates a magnetic flux. Lenz""s law states that the induced emf in a conductor is always polarized in a direction so as to oppose the change that causes the induced emf. Thus, the magnetic flux in the conductive object will oppose the magnetic flux in the coil creating a repulsive magnetic force that acts to push apart the coil and object.
A prior art method of fabrication of MEMS is a multi-user MEMS process (referred to as MUMPs). In general, the MUMPs process provides up to three-layers of conformal polysilicon that are etched to create a desired physical structure. The first layer, POLY 0, is coupled to a supporting nonconductive wafer. The second and third layers, POLY 1 and POLY 2, are mechanical layers that can be separated from their underlying structure by the use of sacrificial layers that separate the layers during fabrication and are removed near the end of the process. The POLY 1 and POLY 2layers may also be fixed to the underlying structure (the wafer or lower POLY 0 or POLY 1 layer as the case may be) through openings, or vias, made by etching.
The MUMPs process also provides for a final top layer of 0.5 xcexcm thick metal for probing, bonding, electrical routing and reflective mirror surfaces.
Further information of the MUMPs process is available from Cronos Microsystems, Inc., 3021 Cornwallis Road, Research Triangle Park, N.C.
In preferred embodiments, the device of the present invention is fabricated by the MUMPs process. However, the MUMPs process may change as dictated by Cronos Microsystems, Inc., or other design considerations. The MUMPs fabrication process is not a part of the present invention and is only one of several processes that can be used to make the present invention.
The present invention overcomes the problems of the prior art by providing a microelectromechanical systems actuator that uses very little space on a substrate, is inexpensive to fabricate, and is very reliable. In addition, the present invention provides a billboard that does not require electrical connection to the substrate or a power source, the invention does not require magnetic materials, and the fabrication is compatible with existing integrated circuit fabrication methods.
In preferred embodiments of the actuator of the present invention, the actuator includes a substrate, a magnetic flux generator that provides a magnetic flux along a flux direction, and a substantially planar device, such as a panel, that is hingedly coupled to the substrate so that the panel can pivot between a first position and a second position. Further, the panel has an electrically conductive portion, or region, such as a metallic ring formed on its surface.
Activation of the magnetic flux generator creates a time-varying magnetic flux along the flux direction that induces an electromotive force (emf) in the conductive portion of the panel. The emf in the panel creates a second magnetic flux that creates a repulsive magnetic force between the magnetic flux generator and the panel that moves the panel from the first position to the second position.
In preferred embodiments, the magnetic flux generator is a conductive coil fabricated on the substrate so as to encircle one or more panels. The coil may also be located between the substrate and the panel. Coupled to the coil is a power source that provides a time-varying electrical current, such as a current pulse. As the current pulse is conducted in the coil, a time-varying magnetic flux is created in the coil that induces the emf in the conductive region of the panel.
Preferred embodiments of the present invention also include a flat spring that holds the panel in the second position. The preferred flat spring is a cantilevered arm that is biased against an extension of the panel. As the panel moves, the flat spring presses against the panel extension, creating a drag force. When the panel reaches a desired second position, the flat spring moves into a cutout, or receptacle, of the extension and holds the panel in the desired position. The flat spring may also be configured so that the drag force acts to hold the panel whenever the magnetic force is not sufficient to overcome the drag force, thus holding the panel in any desired position between the first and second positions.
In preferred embodiments, the panel is hinged to the substrate so as to pivot relative to the substrate. Thus, the panel can move from a first position that is parallel to the substrate, to a second position that is oblique or orthogonal to the substrate. Alternatively, the panel is coupled to the substrate by biased fingers, or a scaffold, that guides the movement of the panel when the magnetic force moves the panel. Such alternative couplers may be configured so that the panel remains substantially parallel to the substrate and moves upward with little or no pivoting.
The present invention also provides a method of moving the panel between first and second positions. In the preferred steps of the method, a panel is fabricated on a substrate so that the panel can move between the first and second positions. An electrically conductive region is provided on panel.
The method further includes fabricating the coil on the substrate so that a magnetic flux in the coil is directed at the panel. To move the panel, the coil is energized by a current so as to create a time-varying magnetic flux in the coil that induces the electromotive force (emf) in the conductive region of the panel and the emf generates a magnetic flux in the panel. Lenz""s law requires that the panel magnetic flux opposes the coil magnetic flux thereby creating a repulsive magnetic force that moves the panel from the first position to the second position.
The preferred method also includes applying a drag force on the panel when the panel moves. The method further includes holding the panel in the second position after the magnetic force moves the panel to the second position.
Other features, means, and steps of the invention are disclosed in the detailed description of the invention and the figures that form a part of the specification.